Evaluate or Simplify the Expression Without Using a Calculator $\mathrm { pH }$

Evaluate or simplify the expression without using a calculator.
-The $\mathrm { pH }$ of a solution ranges from 0 to 14 . An acid has a $\mathrm { pH }$ less than 7 . Pure water is neutral and has a $\mathrm { pH }$ of 7. The $\mathrm { pH }$ of a solution is given by $\mathrm { pH } = - \log \mathrm { x }$ where $\mathrm { x }$ represents the concentration of the hydrogen ions in the solution in moles per liter. Find the $\mathrm { pH }$ if the hydrogen ion concentration is $1 \times 10 ^ { - 4 }$ .

A) 4
B) 10
C) $- 4$
D) $- 10$